Journal of Geosciences, 60 (2015), 259–267

DOI: 10.3190/jgeosci.203

Original paperJežekite, Na8[(UO2)(CO3)3](SO4)2·3H2O, a new uranyl mineral from
Jáchymov, Czech Republic
Jakub Plášil1*, Jan Hloušek2,†, Anatoly V. Kasatkin3, Dmitry I. Belakovskiy3, JiříČejka4, Dmitry Chernyshov5
1

Institute of Physics, Academy of Sciences of the Czech Republic v.v.i, Na Slovance 2, 182 21 Prague 8, Czech Republic; plasil@fzu.cz
U Roháčových kasáren 24, 100 00 Prague 10, Czech Republic
3
Fersman Mineralogical Museum of the Russian Academy of Sciences, Leninsky Prospekt 18-2, 119071 Moscow, Russia
4
Department of Mineralogy and Petrology, National Museum, Cirkusová 1740, 193 00 Prague 9, Czech Republic
5
Swiss–Norwegian Beamlines at the European Synchrotron Radiation Facility, 38000 Grenoble, France†
deceased on April 27, 2014
* Corresponding author2Ježekite (IMA2014-079), Na8[(UO2)(CO3)3](SO4)2·3H2O, is a new uranyl carbonate-sulfate mineral from Jáchymov,Western Bohemia, Czech Republic. The new mineral was found on samples from the Geschieber vein in the Svornost
mine. It occurs as a crystalline crust composed of thin, bladed prismatic crystals of yellow to sulfuric yellow color ona gangue along with andersonite, čejkaite, schröckingerite and ubiquitous gypsum. It is a supergene, low-temperaturemineral formed by hydration–oxidation weathering of uraninite associated with post-mining processes. Ježekite is he­xagonal, space group P–62m, with unit-cell parameters a = 9.0664(11), c = 6.9110(6) Å and V = 491.97(12) Å3, Z = 1.
Crystals are thin blades elongated along [001]. Crystals exhibit the forms {001}, {1–11}, {100} and {010}, commonly
forming twins/intergrowths with a twin plane parallel to [001]. Ježekite is light yellow to sulfuric yellow and has avery pale yellow streak. It exhibits a bright greenish white fluorescence under both long-wave and short-wave UV. It istransparent with a vitreous to pearly luster. The mineral has a Mohs hardness ~2; it is brittle, with uneven fracture anda perfect cleavage on {001} and along [010]. The calculated density based on the empirical formula is 2.966 g/cm3.
The mineral is optically uniaxial (+), with ω = 1.484(2) and ε = 1.547(2) (589 nm). It is non-pleochroic. The chemicalcomposition of ježekite (wt. %, electron-microprobe) is: Na2O 27.92, SO3 18.49, UO3 32.85, CO2 (calc.) 15.08, H2O(calc.) 6.17, total 100.51, which yields the empirical formula Na7.88(UO2)(CO3)3(S1.01O4)2·3H2O (based on 22 O apfu).
Prominent features in the Raman spectrum include the O–H stretching vibrations, symmetric stretching vibrations of(UO2)2+ ions, and stretching and bending vibrations of symmetrically non-equivalent CO3 groups and highly disordered
SO4 tetrahedra. The eight strongest powder X-ray diffraction lines for ježekite are [dobs Å (Irel.) (hkl)]: 7.861(59)(100),
6.925(20)(001), 5.193(100)(101), 4.534(44)(110), 3.415(23)(201), 2.751(17)(112), 2.728(20)(211), 2.618(25)(300). The
crystal structure of ježekite (R = 0.043 for 444 reflections with Iobs > 3σ[I]) contains finite uranyl tricarbonate clusters
linked through the Na–O bonds to form sheets of the composition {Na2[(UO2)(CO3)3]}2– parallel to (001). The adjacent
sheets of polyhedra are also linked through Na–O bonds to the six Na2 atoms and highly disordered sheets of composition {[(SO4)2(H2O)3]}4– into a sandwich-like structure. The new mineral is named after Professor Bohuslav Ježek
(1877–1950), a prominent Czech mineralogist and crystallographer.
Keywords: ježekite, new mineral, uranyl carbonate-sulfate, crystal structure, Jáchymov
Received: 17 September, 2015; accepted: 9 December, 2015; handling editor: J. Sejkora
The online version of this article (doi: 10.3190/jgeosci.203)  contains supplementary electronic material.

1. Introduction
Uranyl carbonates are important alteration products ofhydration–oxidation weathering of uraninite (Finch andMurakami 1999; Krivovichev and Plášil 2013; Plášil
2014), which are of great environmental importance dueto the extensive thermodynamic stability of dissolved
uranyl carbonate complexes in the solutions. Therefore,
the uranyl carbonate complexes are often responsible forincreased mobility of U (as U6+, in the form of the uranylion, UO22+), in particular under weakly acidic to alkalineconditions (Langmuir 1978). The increased activity of
CO2 in solution is due to dissolution of common gangue
carbonates or from atmospheric CO 2 in descending/meteoric waters. Uranyl carbonates most frequently occur as efflorescence on mine walls, adits and tunnels, ascharacteristic minerals formed as recent or sub-recent
phases due to post-mining weathering (Plášil 2014 andreferences therein). However, also “old” in-situ formed
uranyl carbonates are known as constituents of massive
aggregates of uranyl minerals called gummites (Plášil etal. 2006, 2010). Similarly, several well-known uranyl
www.jgeosci.org

Jakub Plášil, Jan Hloušek, Anatoly V. Kasatkin, Dmitry I. Belakovskiy, Jiří Čejka, Dmitry Chernyshov

Fig. 1 Ježekite from Jáchymov. a – Typical massive crystalline crust on weathered gangue. Width of image is 4 mm. b – Detailed view of crystalline aggregates composed of thin, long hexagonal crystals. Width of image is 2.5 mm. (Both photographs by P. Škácha).

carbonates from U deposits of Democratic Republic ofCongo such as wyartite, sharpite and roubaultite are mostprobably also of supergene in-situ (old) weathering origin, being associated with alteration of the U ore-bodies
in the geological past.
Here we report on ježekite (pronounced ‘ye zhe kait’;
Cyrillic – ежекит), which is a new uranyl carbonatesulfate mineral from Jáchymov (Joachimsthal), Czech
Republic. The new mineral and name were approvedby the Commission on the New Minerals, Names andClassification of the International Mineralogical Association (IMA2014-079). The new mineral is named after
Professor Bohuslav Ježek (1877–1950), Czech crystallographer and mineralogist, professor of both Charles
University in Prague and Technical University of Mining
in Příbram. Bohuslav Ježek was a student of Professor
Karel Vrba at the former Karl-Ferdinand University in
Prague (later Charles University), after whom vrbaite isnamed (Ježek 1912). Professor Ježek obtained veniumdocendi at the Charles University and started, for the firsttime in Czechia, experimenting with the diffraction of
X-rays on crystals together with Dr. Karel Teige. They
also began teaching crystallography at the University in
1922. Later, Professor Ježek moved on to the Technical
University of Mining in Příbram, where he was appointed
as a regular Professor of Mineralogy. Besides exceptional
lecture texts and books (used by students long after his
death), Professor Ježek translated Agricola’s classicalwork “Twelve Books on Mining” from Latin to Czech (in1933). Among his mineralogical works, a paper on johannite from Jáchymov (Ježek 1916) is of particular interest.
It is noted that in 1914 another Czech mineralogist, Prof.
František Slavík, had already named a phosphate from
Greifenstein, Germany (Slavík 1914a, b) after Bohuslav
Ježek. However, further analyses showed that “ježekite”
of Slavík was the same as Na-rich morinite and, thus,
the former mineral was discredited (Fischer 1962). Since
more than fifty years have passed after that discrediting,260

re-use of the same name is allowed by CNMNC in accordance with its current rules (Nickel and Grice 1998).
The holotype specimen is deposited in the systematiccollection of the Fersman Mineralogical Museum of theRussian Academy of Sciences, Moscow, Russia, under
the catalogue number 94620.

2. OccurrenceJežekite was found on two specimens only collectedduring the 1990’s by one of the authors (JH) at the Geschieber vein of the Svornost mine, Jáchymov, western
Bohemia, Czech Republic. Unfortunately, there are nolabels specifying the exact place where these specimens
were collected. According to the mineral assemblage ofthese samples, we only infer that they came from the 10th
level of the mine. A description of the locality of Jáchymov and its geological setting has been already given indetail elsewhere (e.g., Ondruš et al. 1997, 2003; Tvrdý
and Plášil 2010; Hloušek et al. 2014). The Jáchymov ore
district is a classic example of the Variscan hydrothermalvein type of deposit, the so-called “five-elements formation”, Ag–Bi–Co–Ni–U. Jáchymov is the type locality
for 45 minerals and more than 430 others have been
identified there.
Minerals found in direct spatial association withježekite include Na-rich uranyl carbonates: andersonite,čejkaite, schröckingerite and also natrozippeite. Minerals
putty several fragments covering the footwall of an old
mining adit. They are of supergene origin and formed due
to alteration during post-mining processes.

3. Physical and optical propertiesJežekite forms markedly thin, fine, bladed to acicular
crystals up to 0.2 mm long, tightly packed in isolatedJežekite, a new uranyl mineralaggregates up to 0.5 mm across (Fig. 1) and/or massive
veinlets consisting of these crystals. They were commonly found to be curved by torsion. Crystal forms{001},{1–11},{100},{010} were observed on crystals
elongated on [001]. Common twinning is on (001) plane.
Ježekite is pale to sulfur yellow in crystals and intensive
sulfur yellow in larger aggregates with a pale yellow
streak. Crystals are transparent with a vitreous to pearlyluster. They are brittle, with a perfect cleavage on (001)
and a good cleavage along (100), and have uneven fracture. The Mohs hardness is estimated at ~2. A density of
2.966 g/cm3 was calculated using the empirical formula
and unit-cell dimensions from single-crystal X-ray data.
Ježekite shows bright greenish white fluorescence underboth long- and short-wave UV; however, it is stronger under short-wave UV. The new mineral is optically uniaxial
positive, with ω = 1.484(2) and ε = 1.547(2) (589 nm).
It is non-pleochroic; however, it shows some pseudoabsorption effects due to the high birefringence. The
elongation direction of the acicular crystals is negative;
extinction is straight. The Gladstone-Dale compatibility,
1 – (Kp/Kc), is fair (0.069) for the empirical formula andthe single-crystal unit-cell.

4. Chemical composition

Mean (n = 9)
Range
27.92
27.12–28.46
Na2O
SO3
18.49
17.62–19.47
UO3
32.85
32.38–33.63
CO2
15.08*
H 2O
6.17*
total
100.51* calculated from the structure
SD – standard deviation

SD
0.49
0.59
0.44

Standard
AlbiteBaSO4 (synth.)
UO2 (synth.)

on 22 O apfu). The simplified formula, Na8[(UO2)(CO3)3](SO4)2·3H2O, requires Na2O 28.15, CO2 14.98, SO3 18.22,
UO3 32.51, H2O 6.14, total 100 wt. %.
Ježekite is slightly soluble in a cold H2O and readilysoluble in 10% HCl acid.

5. Raman spectroscopy
A Raman spectrum of ježekite (Fig. 2) was collectedin the range 50–4000 cm –1 using a DXR dispersive
Raman spectrometer (Thermo Scientific) mounted ona confocal Olympus microscope (100× objective). The
Raman signal was excited by a 532 nm diode-pumped
solid-state laser and detected by a CCD detector. The
experimental parameters were: 5 s exposure time, 32
exposures, 400 lines/mm grating, 50 mm slit spectrograph aperture and 2.5 mW laser power level. The
instrument was set up by a software-controlled calibration using multiple neon emission lines (wavelength
calibration), multiple polystyrene Raman bands (laser

Raman Intensity (au)

The chemical composition of ježekite was determinedusing a CamScan4D scanning electron microscope (SEM)
equipped with an Oxford Link ISIS energy-dispersive
X-ray spectrometer. An operating voltage of 15 kV wasused for the analysis with a beam current of 500 pA anda beam rasterizing area of 8 × 8 μm, since ježekite wasfound to be extremely unstable
under the electron beam dueto the presence of componentsthat are volatilized readily (Naas well as CO3 and H2O). The
molecular H2O content was notdetermined directly, becauseof the paucity of pure material
available for thermal analysis.
The H2O content was calculated
from the stoichiometry in turnobtained from the structure
model. The presence of H 2O
was confirmed independently
by Raman spectroscopy.
The empirical formula ofježekite, calculated as a meanof nine representative spot analO–H stretchingyses (Tab. 1), is Na 7.88[(UO 2)
vibration(CO 3) 3](S 1.01O 4) 2·3H 2O (based

Tab. 1 Results of chemical analyses (in wt. %) of ježekite

Fig. 2 The Raman spectrum of ježekite.

4000

3000

2000

1500

Raman shift (cm–1)

1000

500

261

Jakub Plášil, Jan Hloušek, Anatoly V. Kasatkin, Dmitry I. Belakovskiy, Jiří Čejka, Dmitry Chernyshov

frequency calibration) and standardized white-lightsources (intensity calibration).
Spectral bands at 3620 and 3380 cm–1 are attributed toν O–H vibrations of symmetrically non-equivalent H2O
molecules. According to the correlation published by
Libowitzky (1999), the O–H…O hydrogen bond lengths
vary between 3.20 and 2.90 Å. Bands at 2740 and 1710
cm–1 may be related to the overtones or combination
bands. Bands at 1656 and 1600 cm–1 were assigned to theν2 (δ) bending vibrations of structurally non-equivalent
H2O molecules. Very weak bands in the region from 1300
to 1600 cm–1 are, however, related to the split doubly
degenerate ν3 (CO3)2– antisymmetric stretching vibrations. Bands at 1195, 1130 and 1110 cm–1 are attributed
to the triply degenerate ν3 (SO4) antisymmetric stretchingvibrations, and two bands at 1060 and 1050 cm–1 to theν1 (CO3) symmetric stretching vibrations. According to
Jolivet et al. (1980), the magnitude of the splitting of the
Tab. 2 Powder diffraction data for ježekite
dcalc.

Icalc

h

k

l

Irel.

dobs.

59
7.861
7.857
20
6.925
6.918
100
5.193
5.192
44
4.534
4.536
14
3.926
3.928
12
3.792
3.793
11
3.460
3.459
23
3.415
3.416
8
3.166
3.166
12
2.968
2.970
17
2.751
2.751
20
2.728
2.729
25
2.618
2.619
3
2.596
2.596
7
2.449
2.449
2
2.305
2.306
13
2.269
2.268
5
2.254
2.253
3
2.213
2.213
4
2.177
2.179
8
2.153
2.155
1
2.088
2.088
8
2.080
2.078
3
2.056
2.056
2
1.9895
1.98871
1.96471.96428
1.8973
1.89672
1.8841
1.889551.84401.84372
1.82201.821441.80261.802541.74441.74425
1.73101.73075
1.72831.7296d values quoted in Å

40
26
100
40
14
12
18
27
12
10
21
28
23
4
10
3
17
8
8
6
12
2
12
6
5
2
12
5
8
7
6
8
5
4

1
0
1
1
2
1
0
2
1
2
1
2
3
2
3
0
2
2
1
3
2
3
3
1
2
4
2
4
3
2
3
3
3
0

0
0
0
1
0
1
0
0
0
1
1
1
0
0
0
0
2
1
0
1
2
0
1
1
0
0
2
0
1
1
2
2
0
0

0
1
1
0
0
1
2
1
2
0
2
1
0
2
1
3
0
2
3
0
1
2
1
3
3
0
2
1
2
3
0
1
3
4

3
3
1
2
3
2
2
1
2
2
1
2
1
1
1
2
1
1
1
1
2
1
1
1
1
1
1
1
1
2
1
1
1

1.71471.70891.68971.6644
1.6173
1.59891.5841
1.5712
1.5362
1.5324
1.51191.49491.48471.4772
1.45211.44381.42051.41081.38551.38281.37601.3646
1.36141.3552
1.30991.3064
1.2984
1.2863
1.26971.24791.23761.22451.2179

Irel.

262

dobs.

doubly degenerate ν3 (CO3)2– antisymmetric stretching vibrations (1550, 1375, 1355 cm–1) supports conclusions of
the X-ray crystal structure analysis: the carbonate planargroups are linked bidentately in the equatorial plane of
the uranyl hexagonal bipyramids. A band at 996 cm–1 isattributed to the ν1 (SO4) symmetric stretching vibration.
A very weak band at 896 cm–1 may be connected withthe ν3 (UO2)2+ antisymmetric stretching vibration and thevery intense band at 825 cm–1 to the ν1 (UO2)2+ symmetricstretching mode. Anyway, the possibility of coincidenceof the bands related to the ν1 (UO2)2+ and the ν2 (CO3)cannot be excluded. According to the empirical relation
given by Bartlett and Cooney (1989), the U–O bondlengths in the uranyl ion, inferred from the stretching
wavenumbers of the ν1 and ν3 bands are approximately~1.79 Å. The weak bands at 731 and 715 cm–1 are assigned to the ν4 (δ) doubly degenerate (CO3) in-planebending vibrations. Bands at 688, 629 and 622 cm–1 are
attributed to the triply degenerate ν4(δ) (SO4) bending vibrations. Bands at458
and 379 cm–1 may be connected
Icalc h k ldcalc.
with the doubly degenerate ν 2 (δ)
1.71455
4 1 0(SO) bending vibrations, while those
1.7080
2
4 0 2
4
at
277
and 248 are due to the doubly
1.68913
1 0 4
degenerate ν 2 (δ) (UO 2) 2+ bending
1.664144 1 1
vibrations. The remaining bands at
1.61706
2 2 3188, 161 and 85 cm–1 may be assigned
1.59855
3 2 2
1.583843 1 3
to ν (U–Oligand) stretching and δ (Oli1.5713
1
5 0 0
UOligand) and δ (OUOligand) bending
gand
1.53613
4 1 2
vibrations (Volod’ko et al. 1981).

1.53231.51201.49451.48481.4772
1.45171.44321.4201
1.41111.38551.38261.37531.36441.36271.35471.30951.3066
1.29851.2866
1.26971.24801.23781.22461.2176

2
2
4
1
2
4
3
3
2
1
2
4
2
2
3
2
2
1
2
2
3
2
1
2

5
3
2
4
3
4
3
3
5
3
5
2
4
1
3
6
5
5
6
4
3
5
6
4

0
3
1
2
3
2
0
2
1
3
1
2
2
0
1
0
1
0
0
3
2
2
0
1

1
0
4
0
1
1
4
3
0
2
1
4
2
5
4
0
2
3
1
1
4
1
2
4

6. X-ray crystallography
and structure
determination

6.1. Powder diffraction
X-ray powder diffraction data (Tab. 2)
were obtained from a hand-pickedsample using a PANalytical Empyrean diffractometer equipped with a
PIXcel3D detector using CuKα radiation (45 kV, 40 mA) and operating in
Debye–Scherrer geometry provided
by focusing Göbel mirror optics. Data
were collected in the range 3–70° 2θ,with a step size of 0.01° and counting time of 2 s per step, using an
accumulation of 40 scans to improve
the intensity statistics. Positions andintensities of diffraction profiles wererefined using a pseudo-Voigt shapefunction with the High-Score pro-Ježekite, a new uranyl mineralgram (PANalytical, Almelo,B.V.). Unit-cell parameters
were refined by least-squares
with the Celref program (Laugier and Bochu 2003). The
theoretical pattern, used forindexing the experimental dataset, was calculated from thestructure data using PowderCell (Kraus and Nolze 1996).
Refined unit-cell parametersof ježekite obtained frompowder data are a = 9.072(2),c = 6.9182(1) Å, with V =493.1(1) Å3 and Z = 1.

6.2.	Single-crystal X-ray
diffraction andstructure solution

Tab. 3 Crystallographic data and refinement details for ježekite
Crystal data
FormulaCrystal system
Space group
Unit-cell parameters: a, c [Å]Unit-cell volume [Å3]Z
Calculated density [g/cm3]
Crystal size [mm]Na8[(UO2)(CO3)3](SO4)2(H2O)3
hexagonal
P6̄2m
9.0664(12), 6.9110(6)9.08022(7), 6.92071(16)491.97(10)494.168(12)1
2.971
0.10 × 0.03 × 0.02

Data collection
PILATUS@SNBL diffracOxford Diffraction Gemini withtometer, BM01A ESRF,
Atlas detector
Pilatus 2D detector
Temperature [K]302
300
Radiation, wavelength [Å]MoKα, 0.71073 (50 kV, 30 mA) Synchrotron, 0.68884
θ range for data collection [º]2.95−29.18
2.51–31.37
h = –11→10, k = –12→11,h = –13→13, k = –13→13,
Limiting Miller indicesl = –8 → 9l = –6 → 6
Axis, frame width (º), time per frame (s) ω, 0.9, 310
Φ, 1, 1
Total reflections collected
3392
4551
Unique reflections
444
539
Unique observed reflections, criterion
420, [I > 3σ(I)]539, [I > 3σ(I)]Absorption coefficient [mm–1], type8.75; Gaussian
8.75/multi-scan
0.526/15.533
0.898/1
Tmin/Tmax
0.116
0.046
Rint
406
395
F000
Diffractometer

A prismatic crystal ofježekite, with dimensions
0.10 × 0.03 × 0.02 mm, wasselected under the microscope and examined using an
Oxford Diffraction Gemini
single-crystal diffractometer
Full-matrix least-squares on F2
with an Atlas CCD detec- Structure refinement by Jana2006
No.
of
ref.
param.,
restraints,
constraints
38,
0,
0
33, 0, 0
tor using monochromatized
R,
wR
(obs)
0.0426,0.08320.0431, 0.1051
MoKα radiation, with a fibreR,
wR(all)
0.0454,0.0846
0.0431, 0.1051
optic Mo-Enhance collimator.
GOF
obs/all
1.43,
1.41
2.43, 2.43
According to single-crystal
σ, w =1/(σ2(I)+0.0016I2)
Weighting scheme, weights
σ, w =1/(σ2(I)+0.0004I2)
X-ray data, ježekite is hexa­–1.37, 1.46
–3.18/4.31
Largest diff. peak and hole (e–/Å3)
gonal with a = 9.0664(11), c =6.9110(6) Å, V = 491.97(12)the indices of agreement. The dataset from ESRF, with
Å3 and Z = 1. Of the 3392 collected reflections, 444
better intensity statistics, clearly demonstrated that thewere unique and 404 were classified as observed based
crystal investigated is a multi-domain split crystal. Nevon the criterion [Iobs > 3σ(I)]. Data were corrected forertheless, introduction of a split crystal (modelled as a
the Lorentz effect, polarization factor and background;non-crystallographic rotational twin) into the refinement
also Gaussian correction for absorption was applied in
did not lead either to a substantial improvement of the
Jana2006 program (Petříček et al. 2014). In order tofit or a more acceptable model. The data were checkedobtain a better dataset, the same crystal was investigated
for twinning by merohedry or pseudomerohedry (reticuat the European Synchrotron Radiation Facility (ESRF,
lar), but again the fit did not provide reasonable results
Grenoble, France) at room temperature using the PILA(negative values of twin fractions etc.). Due to the simiTUS@SNBL diffractometer at the BM01A end station
lar results provided by both datasets we decided to baseof the Swiss–Norwegian Beamlines; the wavelength
our interpretation and discussion of the structure on theof the synchrotron radiation was set to 0.70135 Å. The
results from the laboratory diffractometer. The details ofdata were collected with a single Φ scan with an angularthe data collection and refinement for both datasets are
step of 0.1° in a shutter-free mode with the Pilatus2M
given in Tab. 3.
detector. The raw data were pre-processed with SNBL
The crystal structure of ježekite was solved by the
TOOLBOX and the integral intensities were extracted
charge-flipping algorithm implemented in the Superflip
from the frames with the CrysAlisPro software (Rigaku).
program (Palatinus and Chapuis 2007) and subsequently
However, the dataset provided results very similar torefined using the software Jana2006 (Petříček et al. 2006,
the laboratory data in terms of the refined structure and263

Jakub Plášil, Jan Hloušek, Anatoly V. Kasatkin, Dmitry I. Belakovskiy, Jiří Čejka, Dmitry Chernyshov

Tab. 4 Atom coordinates, displacement parameters and bond-valence sums for the crystal structure of ježekite
Atom

Occ.

BV

x/a

y/b

U1
6.02(7)00Na11.00(2)0.666667 0.333333
Na2
0.81(1) –0.3631(8) 0
C1
4.1(1)
00.3173(18)S10.333 6.3(2)0.6736(9) 0.4041(9)O12.42(4)
0.666667 0.333333
O2
2.08(5) –0.1394(15) 0.1730(16)O3
1.64(4)00O41.97(8)00.4556(12)O5
0.5
1.24(4)0.599(3)0.494(3)O6
0.5
0.244(4) 0.819(3)0.700(3)O7
0.1667 1.92(6)0.814(3)0.532(3)Occ. – occupancy; BV – bond-valence sum (in vu)

z/c

Ueq/Uiso (Å2)

U11

U22

U33

U12

U13

0.5
0.5
0.7532(13)0.5
00.176(2)0.50.2404(19)
0.5
0
0
0

0.0204(2)0.0221(18)0.022(3)0.026(4)0.0228(15)0.048(2)0.090(8)0.031(4)0.085(7)0.023(3)0.030(4)0.022(3)0.0115(3)0.097(5)0.083(4)0.034(10)0.0115(3)0.097(5)0.248(13)0.016(6)0.0106(5)0.010(5)0.016(5)0.010(11)0.00574(17)0.048(2)0.124(7)0.017(5)000.000(3)02014) with the full-matrix least-squares refinement basedon F2. Superflip output suggested a solution in the hexa­
gonal highest space-group P6/mmm. However, the structure has lower symmetry, P6̄2m, as documented by therefinement; even though the real symmetry can be lower
still (see below). The hexagonal symmetry is consistent
with the point group of the sub-lattice in ježekite, represented by the U and Na atoms in the structure. We notethat the ježekite structure as presented here is an average
one, containing highly positionally and occupationallydisordered SO4 groups in the interlayer. Nevertheless, astructure refinement in lower symmetry space groups did
not lead to any improvement in the fit to the data. Therefore, we decided to present the model with the disordered
SO4, since refined values for all other atoms turned out
to make physical sense. We also note that the diffraction
intensities are affected 1) by the dominant contributions
from the U atoms and 2) the presence of rotational twin
domains from the split crystal.
The heavy atoms were found in the structure solution
readily and the lighter ones were localized by the difference Fourier syntheses. An attempt to use the rigid-body
approach for the refinement of the disordered (SO4) led tosignificantly worse results than a simple less-constrainedrefinement. The refinement converged with the final
indices of agreement R = 0.0426 and wR = 0.0832 for
420 observed reflections with GOF = 1.43 (Tab. 3).
The atom coordinates, the displacement parameters andbond-valence sums are given in Tab. 4 and selectedinteratomic distances in Tab. 5. The bond-valence sums
were calculated according to Brown (2002), using bondvalence parameters of Burns et al. (1997) and Brown andAltermatt (1985).

6.3. Description of the crystal structure
The single U site in the structure of ježekite is surroundedby eight O atom sites forming a squat hexagonal bipyra264

Tab. 5 Selected interatomic distances (Å) in the structure of ježekite
U1–O2
U1–O2iU1–O2ii
U1–O2iii
U1–O2iv
U1–O2v
U1–O3
U1–O3vi<U–OUr><U–Oeq>2.458(17)2.458(16)2.458(18)2.458(17)2.458(16)2.458(18)1.794(13)1.794(13)
1.794
2.458

Na1–O1Na1–O1vi
Na1–O2vii
Na1–O2viii
Na1–O2ii
Na1–O4vii
Na1–O4viii
Na1–O4ii<Na1–O>

2.240(17)2.240(17)2.786(17)2.786(18)2.786(16)2.6481(19)2.648(13)2.648(13)
2.59

S1–O1
S1–O1xi
S1–O5
S1–O7<S1–O>

1.361(15)1.361(15)1.29(3)
1.22(6)
1.31

C1–O2
C1–O2v
C1–O4<C1–O>

1.287(13)1.287(13)1.25(2)
1.28

Na2–O22.541(10)Na2–O2vi
2.541(10)Na2–O4xxi
2.401(11)
Na2–O5xxii
2.52(3)
Na2–O5v
2.522(18)
Na2–O6xxiii
2.62(2)Na2–O6xxiv
2.62(3)
Na2–O7xxiii
2.249(19)Na2–O7xxiv
2.249(17)<Na2–O>
2.47
O1–O1xi
2.43(2)O3–O6xix
2.90(2)
O1–O5
2.21(3)O3–O6xx2.90(3)O1–O5ix
2.21(2)O5–O5xii
1.65(4)
O1–O5x2.21(3)
O5–O6
1.93(3)
O1–O7
2.02(2)O5–O6xii
2.61(4)O1–O7ix
2.02(3)
O5–O7
1.80(4)O1–O7x2.02(3)O5–O7ix
1.68(4)O2–O2iv
2.717(18)
O5–O7xix
2.76(5)O2–O2v
2.189(16)O6–O6xii
1.88(5)
O2–O4
2.218(16)O6–O6xxv
2.84(3)O3–O6xvi
2.898(18)O6–O7
1.50(4)O3–O6ix
2.90(2)O7–O7ix
2.80(3)O3–O6xvii
2.90(3)O7–O7x2.80(4)O3–O6xviii
2.898(18)
O7–O7xxv
2.92(4)
Symmetry codes: (i) –y, x–y, z; (ii) –x+y, –x, z; (iii) y, x, –z+1; (iv) x–y,–y, –z+1; (v) –x, –x+y, –z+1; (vi) x, y, –z+1; (vii) x+1, y, z; (viii) –y+1,
x–y+1, z; (ix) –y+1, x–y, z; (x) –x+y+1, –x+1, z; (xi) x, y, –z; (xii) y, x,–z; (xiii) x+1, y, –z+1; (xiv) –y+1, x–y+1, –z+1; (xv) –x+y, –x, –z+1;(xvi) x–1, y–1, z; (xvii) –x+y, –x+1, z; (xviii) y–1, x–1, –z; (xix) x–y,–y+1, –z; (xx) –x+1, –x+y, –z; (xxi) –x+y–1, –x, z; (xxii) –y, x–y, z+1;
(xxiii) –x+y, –x+1, z+1; (xxiv) y–1, x–1, –z+1; (xxv) –x+2, –x+y+1, –z.

Ježekite, a new uranyl mineralFig. 3 The structure of ježekite viewed down [001]. The unit cell isshown by red solid lines. The UO 8 hexagonal bipyramids are blue,
CO3 planar groups chelating UO8 are black. Sodium atoms are violet,
S atoms yellow, O atoms shown as small red spheres.

mid. This is one of the typical coordinations for U 6+ inthe solid state in which the two short apical bonds of the
bipyramid constitute the uranyl, UO 22+ ion. Observed
bond lengths for the polyhedra (Tab. 5) are consistent
with those most frequently observed for [8]-coordinatedU6+ (Burns et al. 1997). The uranyl bipyramid is chelatedby three planar CO3 groups (one symmetrically unique Csite) forming a typical uranyl tricarbonate cluster (UTC)[(UO2)(CO3)3]4–. These clusters are linked to the Na1
atoms, occupying 2d sites, to form sheets of composition {Na2[(UO2)(CO3)3]}2–. The Na1 site is [8]-coordi-

nated by six O atoms within the sheet and two O atoms
that are the vertices of the disordered SO4 tetrahedron.
The coordination environment around the second Na
site (Na2) in the structure is much more complicated.
The Na2 site is [9]-coordinated, but some of these ninebonds belong to occupationally disordered O atoms (ofthe SO4 group) and one O atom (O6) clearly belongs toan H2O group, according to the bond-valence analysis(Tab. 3). This H2O is an inverse-transformer group witha [4]-coordinated O atom, with it linked to two Na atoms
and two hydrogen atoms (the H atoms are not present in
the current structure model). There are three positionallydisordered SO4 groups in the structure (generated by thesix-fold axis). The coordination environment of theseSO4 groups is quite complicated and is displayed in Fig.
3; in an average structure they are represented by threemutually exclusive positions. The structure of ježekite
can be viewed as a three-storey sandwich-like structure(Fig. 4) with firm, ordered {Na2[(UO2)(CO3)3]}2– sheets,an alternating interlayer with six (Na2)+ ions plus highly
disordered sheets of composition {[(SO4)2(H2O)3]}4–. The
structural formula of ježekite obtained from the refinement is Na8[(UO2)(CO3)3](SO4)2(H2O)3, Z = 1.

7. Discussion

7.1.	Structure topology, structure relations
The structure of ježekite is unique, but there are several
similarities to other known uranyl minerals and compounds. There is only one known uranyl tricarbonate

Fig. 4 a – The sandwich-like structure of ježekite (left) viewed perpendicular to [001]. The unit cell is shown by black solid lines. The sheets of
UO8 bipyramids and Na1-polyhedra alternate with an interstitial layer containing disordered SO 4 groups and Na2-polyhedra. The stacking sequencecorresponds to the unit-cell parameter c. b – The structure of schröckingerite (Mereiter 1986) showing linkage of SO 4 groups. UO8 bipyramids areblue, NaO6 polyhedra are violet, Ca atoms are displayed in green. In schröckingerite the interstitial complex consists of H-bonded H 2O groups only.

265

Jakub Plášil, Jan Hloušek, Anatoly V. Kasatkin, Dmitry I. Belakovskiy, Jiří Čejka, Dmitry Chernyshovmineral containing (SO4)2– anions in the crystal structure,schröckingerite (Mereiter 1986). The way how the sulfate
tetrahedron is linked in the structure differs from thatin ježekite. In the structure of schröckingerite, the SO4
tetrahedron is shared between three Ca atoms within the
structural sheet, with one non-bridging vertex staggered
towards the interlayer (Fig. 4). Interestingly, the structure of ježekite is somewhat related to that of synthetic
trigonal Na4[(UO2)(CO3)3] (Císařová et al. 2001; Li et al.
2001), in terms of the unit cell metrics. This compoundis a dimorph of monoclinic čejkaite (Plášil et al. 2013)and has not been found in Nature. Hexagonal ježekite has
an a parameter that is similar to the synthetic compoundand also to schröckingerite, and a halved c parameter.
The latter, which represents the stacking of the layers inthe structure, is very close to the stacking in čejkaite, but
the two structures are essentially different. The columnar
stacking of NaOx (most commonly x = 6) polyhedra is,however, a well-known feature from the structures ofNa-containing uranyl carbonates (Císařová et al. 2001; Liet al. 2001; Li and Burns 2001; Plášil et al. 2012, 2013).

7.2.	Note on occurrence
Uranyl carbonates that contain alkali metals such as Na+
or K+ are fairly common in Jáchymov, occurring in various places, where the appropriate conditions occur. Their
origins have been connected with post-mining weathering
processes in the old mining adits with stable humidity
and temperature. The most common Na +-bearing uranyl carbonate mineral in Jáchymov is schröckingerite,
NaCa3[(UO2)(CO3)3](SO4)F(H2O)10 (Ondruš et al. 1997;
Mereiter 1986), which also contains S6+ in the structure,
as ježekite does. However, ježekite is by far rarer, mostprobably due to the very high molar proportion of the
Na+ in the structure.
Acknowledgements. We appreciate kind cooperationof Pavel Škácha, who provided microphotographs ofježekite. We thank Ivan Němec (Faculty of Science,Charles University in Prague) for providing us access to
the Raman microspectrometer. We thank Martin Števko
and an anonymous referee for their comments that greatly
helped improving the manuscript. This research was
financially supported by the post-doctoral grant of theGAČR no. 13-31276P to JP and by the long-term project
DKRVO 2015-02 of the Ministry of Culture of the Czech
Republic (National Museum 00023272) to J.Č.
Electronic supplementary material. Supplementary crystallographic data for this paper are available online at the
Journal web site (http://dx.doi.org/10.3190/jgeosci.203).

266

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